Selectively apertured sheets of material such as rubber, latex, plastic and the like have long been known in the prior art. Typical prior art structures and processes for making them are disclosed in U.S. Pat. No. 2,268,678 issued to Tingey on Jan. 6, 1942; U.S. Pat. No. 2,354,916 issued to Hurt on Aug. 1, 1944; and U.S. Pat No. Re. 23,910 issued to Smith et al. on Dec. 14, 1954. The patent to Tingey discloses a process which comprises applying a latex coagulant to a selected portion of a deposition backing, at least partially drying the coagulant, depositing a layer of latex onto the backing to at least partially coagulate a selected portion of the latex layer, and thereafter concurrently drying or gelling the remainder of the latex layer and piercing only said remainder with a plurality of fluid jets to form permanent perforations therein. The patent to Hurt discloses method and apparatus for embossing plastic sheet material wherein a perforated base may be covered with a cloth mesh which in turn may be covered with a plurality of intersecting threads to create a design. When suction is applied to the interior of the base, the plastic sheet material brought in contact therewith is caused to assume the pattern inherent in the cloth and thread design. The patent to Smith et al. discloses method and apparatus for producing textured films. In the embodiment illustrated in FIG. 4, a woven wire mesh belt has superposed thereon a specially patterned belt such that when the film being processed is subjected to vacuum it is caused to take an impression from the patterned belt.
U.S. Pat. No. 2,776,451 issued to Chavannes on Jan. 8, 1957 also discloses apparatus and method for producing embossed thermoplastic film. Chavannes discloses, in FIG. 2, a perforated vacuum forming roll covered first with wire mesh and then with fabric. Plastic film brought in contact with the surface of the drum is embossed by means of vacuum applied to the interior surface of the drum.
U.S. Pat. No. 3,054,148 issued to Zimmerli on Sept. 18, 1962 discloses a process for producing a perforated thermoplastic sheet which comprises subjecting successive portions of a continuous sheet of thermoplastic material to a uniform softening treatment, passing the softened thermoplastic material into contact with a continuously moving molding element perforated in accordance with a predetermined design, effecting selective plasticity of the sheet in contact with the molding element, subjecting a surface of the thermoplastic sheet to the action of a fluid pressure differential to cause the softened material to flow into the perforations of the molding element, maintaining the pressure differential to effect rupturing of the thermoplastic sheet in accordance with the perforations in the molding element, subjecting the soft molded thermoplastic sheet to a fixing treatment, and continuously removing the molded portions of the thermoplastic sheet from the molding element. The molding element is perforated only in those areas where it is desired to perforate the plastic sheet and is solid in those areas where no perforations are desired.
U.S. Pat. No. 3,312,583 issued to Rochlis on Apr. 4, 1967 discloses a pile-like molded product comprising a base having a plurality of parallel rows of pile formations of pyramidal shape integrally formed on and projecting from a surface thereof, the formations of the respective transversely successive rows being staggered relative to one another in the longitudinal direction of said rows, said base having apertures therethrough separating some of the pile formations of the respective rows from one another, the apertures of a given row being in transverse alignment with pile formations of an adjacent row and being overlapped longitudinally by the ends of such pile formations, the respective pile formations of said given and adjacent rows also longitudinally overlapping one another to provide an integral connection of said respective pile formations at the overlapped portions thereof. Rochlis discloses in FIGS. 21 and 22 mold cavities created by stacking laminar sheets upon one another and enclosing the ends of the cavities by assembling the laminar sheets to a base lamination. Pile-like plastic products are formed by coating the mold cavities thus produced with a softenable material, allowing the softenable material to set up, and stripping the resultant pile-like product from the mold cavity as generally shown in FIG. 19.
U.S. Pat. No. 3,966,383 issued to Bussey, Jr. et al. on June 29, 1976 discloses yet another apparatus for vacuum forming sheet thermoplastic material. The apparatus utilizes an endless, seamless structure as the forming surface. A sheet of heat softened thermoplastic film is passed over a forming screen, the forming screen being supported by a support roll, a drive roll and two seal rolls. A vacuum is applied to the screen between the seal rolls to pull the film into contact with the screen, thereby producing a three-dimensional pattern on the film corresponding to the outer surface of the screen.
Commonly assigned U.S. Pat. No. 4,151,240 issued to Lucas et al. on Apr. 24, 1979 discloses still another preferred method and apparatus for debossing and perforating a running ribbon of thermoplastic film, said patent being hereby incorporated herein by reference. Briefly, the apparatus disclosed in the Lucas et al. patent comprises means for continuously converting a ribbon of thermoplastic film into a debossed and perforated film by directing hot air jets against one surface of the film while applying vacuum adjacent the opposite surface of the film. The aforementioned operations are carried out while maintaining sufficient control of the film to substantially obviate wrinkling and/or macroscopically distending the film. In a particularly preferred embodiment, the debossing and perforating means include a rotatably mounted debossing/perforating cylinder having closed ends, a nonrotating triplex vacuum manifold assembly and hot air jet means. The film contacting surface of the debossing/perforating cylinder exhibits the pattern to be imparted to the plastic film to be treated thereon.
In a particularly preferred embodiment of the Lucas et al. invention, the debossing/perforating cylinder is constructed employing a laminate forming structure of the type generally described in the commonly assigned co-pending patent application of Clifford Radel and Hugh A. Thompson, Ser. No. 206,410, Filed Nov. 13, 1980 and entitled RESILIENT PLASTIC WEB EXHIBITING FIBER-LIKE PROPERTIES AND METHOD AND APPARATUS FOR ITS MANUFACTURE, now U.S. Pat. No. 4,342,314 on Aug. 3, 1982, said patent application being hereby incorporated herein by reference. As is pointed out in the specification of the aforesaid patent application, the laminate forming structure can be utilized to provide selective aperturing of the plastic film, particularly in areas where fluid permeability is desired, and debossing without perforating in those areas where surface texture is desired but fluid permeability is undesirable.
Even with such improved forming structures, however, prior art means for selectively aperturing plastic films have historically been dependent upon such process variables as the temperature of the film, the fluid pressure differential applied to the film and the speed of the overall operation. Thus, heating the film to a greater extent in a preselected area where aperturing is desired has typically been employed to cause rupture of the film in the preselected area when the film is subjected to a uniform fluid pressure differential while it is in contact with the forming structure. An alternative prior art practice has been to apply a greater level of vacuum to those portions of a uniformly heated plastic web to be apertured. Unfortunately, the apertured regions created in the plastic film by either technique are often poorly defined due to the difficulties associated with uniformly controlling the process variables. This is particularly true in situations where the aperturing is to be carried out in a fine pattern, is irregular in shape and/or is discontinuous in the machine direction. Furthermore, such prior art techniques are impractical where it is desired to impart a uniform surface texture and appearance along the entire surface of the web with fluid permeability only at preselected points along the entire surface of the web.
A further difficulty inherent in such prior art processes is that aperturing of the film often results even where it is undesired, particularly where large, relatively weak, unsupported areas are to be debossed by the application of fluid pressure thereto.
Accordingly, it is an object of the present invention to provide method and apparatus for accurately debossing and selectively aperturing a uniformly heated plastic web in nearly any desired predetermined pattern by subjecting the entire surface of said web to a uniform fluid pressure differential on a forming structure of the present invention.
It is another object of the present invention to provide feasible methods for constructing three-dimensional forming structures for imparting a selectively apertured three-dimensional pattern to a heated plastic film which is subjected to a fluid pressure differential while in surface contact therewith.
It is yet another object of the present invention to provide a three-dimensional plastic film precisely apertured only at predetermined points or in predetermined areas, said web exhibiting a substantially uniform overall surface texture and appearance in both the apertured and non-apertured areas thereof.